A growing concern over biological effects from microwave devices has prompted many studies to examine this critical and sensitive issue. While reports from the Soviet Union and other Eastern European countries indicate chronic biobehavioral effects at very low microwave field power densities (less than 1 mW/sq. cm), few studies have been conducted in the United States to study chronic low level microwave exposure. Of the studies that have been conducted in the Soviet Union and in the United States, including our own previous work, chronic microwave exposure effects seem to predominate at microwave frequencies in the 2000-3000 MHz range. Our past work has indicated that selective enhanced microwave absorption in the rat brain takes place in this frequency range. We have termed this effect head resonance. The experiments proposed in this grant application will use a modification of our previous successful numerical techniques to specify the conditions of microwave exposure which maximize the selective absorption in the rat brain. Dosimetric studies will be conducted to confirm this selective absorption and identify hot spots within the rat brain with and without blood flow cooling. Behavioral analyses under both acute and chronic exposure to the most hazardous microwave exposure parameters will then be conducted to specify dose/response relationships on schedule controlled behaviors previously shown to be sensitive to microwave exposure. This approach of numerical specification of hot spots in brain, followed by calorimetric dosimetry verification and subsequent behavioral analyses, will provide a sound basis to evaluate chronic exposure effects.